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Human-monkey embryos spark concern

Researchers have for the first time successfully grown monkey embryos containing human cells – causing widespread ethical debate.

Harnessing pluripotent stem cells

Pluripotent stem cells (PSCs) are capable of indefinite self-renewal in culture and can generate all adult cell types. Researchers have recently used PSCs for interspecies organogenesis via blastocyst complementation. This method represents an alternative approach to evaluate hPSC pluripotency in vivo. It may also provide a promising strategy for regenerative medicine applications, such as the generation of organs and tissues for transplantation.  

For this technique to be successful, human PSCs (hPSCs) must be able to contribute to chimera formation. To date, hPSCs have not been able to consistently and robustly contribute to chimera formation in host animals with a high evolutionary distance from humans e.g., mice and pigs. Nonetheless, researchers have until now explored the use of hPSCs for chimera studies in host species evolutionary close to humans. In previous work, researchers have identified that human extended PSCs (hEPSCs) demonstrate improved chimeric capability in mouse embryos.  Yet, their chimeric competency in other species has not been determined.

Human-monkey embryos

In this study, published in Cell, researchers studied the chimeric competency of hESPCs in cynomolgus monkey embryos cultured ex vivo. They specifically injected monkey embryos with human stem cells, observing that they could divide and grow together in a dish. The researchers found that at least three embryos survived to 19 days after fertilisation.

While this study has certainly hit the headlines and divided developmental biologists, the team hope that this discovery could help better understand human biology and disease. In addition, they hope that it could lead to animals being used to grow organs for human transplantation.

 Juan Carlos Izpisua Belmonte, a professor at the Salk Institute and co-author on the study, expressed:

“Our goal is not to generate any new organism, any monster.

And we are not doing anything like that. We are trying to understand how cells from different organisms communicate with one another.”

Others have questioned why there was a need to experiment on closely related primates – as they are not used as model animals like mice and rodents are. Non-human primates are protected by stricter research ethics rules. Meanwhile, many have questioned the status and identity of the resulting hybrid.

Later next month, the International Society for Stem Cell Research (ISSCR) is set to publish revised guidelines for stem-cell research. These guidelines will address non-human primate and human chimeras.

Image credit: By tmcphotos –

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Chimera / Embryo / Model